1. Field of the Invention
The present invention relates to an electrophotographic apparatus, and particularly to an electrophotographic apparatus capable of controlling the darkness of a copied image in connection with that of an original.
2. Description of the Prior Art
In such an electrophotographic apparatus, a light receiving element is used to receive light from an original to be copied and to generate a signal corresponding to the amount of received light. This signal is used to control the copied image with respect to its darkness. Thus, the copied image will have proper darkness in connection with the darkness in the original.
Japanese Laid-open Patent Application No. 42856/1975 which corresponds to U.S. Pat. No. 3,926,518 discloses such a light receiving element which is disposed on a slitted plate located adjacent to a photosensitive member. Japanese Laid-open Patent Application No. 38718/1973 discloses a light receiving element located across the optical path of a light beam which has been split from an imaging light beam by a half mirror and transmitted through the same, or a light receiving element which is disposed to receive a light from an original through a lens other than an imaging lens through which the original is imaged on a photosensitive member. In these prior art arrangements, the darkness of only a portion of the original can be detected so that the detected information will not match the information of darkness in the overall surface of the original. If the information of darkness in the overall surface of the original is required, an elongated light receiving element or a plurality of light receiving elements must be used resulting in various disadvantages such as an increased cost and others.
Japanese Laid-open Patent Application No. 36725/1979 which corresponds to U.S. Pat. No. 4,200,391 discloses a light receiving element located adjacent to an original placing plate. This arrangement also requires a plurality of light receiving elements if the information must be taken throughout a slit. Further, an additional illuminating device other than the exposure illumination system is required resulting in a complicated structure. Japanese Laid-open Patent Application No. 107270/1981, which corresponds to U.S. Pat. No. 4,354,758 discloses a light receiving element which is disposed behind a lens, in which, however, there is no disclosure as to the part of the original from which the light is received by the light receiving element.